This invention relates to a method for near real-time crustal deformation monitoring using long-baseline radio interferometry.
There has been a continued and growing interest using long baseline radio interferometry for monitoring crustal deformation of the earth for prediction of earthquakes. See "Geophysical Applications of Long Baseline Radio Interferometry," by I. I. Shapiro and C. A. Knight in Earthquake Displacement Fields and the Rotation of the Earth, edited by L. Mansinha, et. al., and published by D. Reidel, Dordrecht, Netherlands, 1970. The present inventor has made a study of the feasibility of radio interferometry in this respect and the results were reported in a paper titled "Radio Interferometry for International Study of the Earthquake Mechanism", Acta Astronantica, VOL. 1, pp. 1427- 1444, Perpamon Press (1974). The technique is not unlike that employed in stellar interferometers. It is operable on a very wide range of baseline lengths from 100 m to intercontinental separations. The term "Astronomical Radio Interferometric Earth Surveying" has been adapted for the technique, now often referred to by the acronym ARIES described in that report.
A precision geodetic measurement system based on ARIES has been designed and implemented through the use of a 9-m transportable antenna and fixed antennas, such as the NASA 64-m antenna of the Deep Space Communication Complex at Goldstone, California, and the 40-m telescope of the Owens Valley Radio Observatory. The system requires extragalactic random (quasar) radio signals received by the two antennas on a very long baseline to be recorded on magnetic tape for off-line cross correlation. The system will detect subtle motions of the Earth's crust in three dimensions. Such motions are believed to precede an earthquake. If that is so, then a reliable earthquake prediction technique could be developed. The key to the system is the capability of measuring the difference in arrival of identical quasar radio signals at the two antennas on the baseline using atomic clocks as timing references and high speed computer techniques for cross correlation. The problem in adapting the system to real-time monitoring, or to near real-time monitoring, using quasar interferometry is cumbersome for real-time observations because of the need for utilizing wideband data communications lines and a plurality of quasar sources to eliminate the effects of system drifts and achieve full three dimensional measurements.